Most of power storage modules include a plurality of power storage elements connected in series. Even though the plurality of power storage elements are of the same type, they are not identical to each other in characteristics, and have their own unique characteristics. This is attributed to inevitable factors such as variations in conditions during manufacture and the difference in the rate of deterioration. Accordingly, for example, the power storage element being the smallest in capacity among the plurality of power storage elements connected in series tends to be overcharged or overdischarged. When overcharge or overdischarge of a power storage element repeatedly occurs, the power storage element further deteriorates, impairing the stability of the power storage module.
Under the circumstances, there is a known system which regulates the voltage for each of a plurality of power storage elements to fall within a range from an operation-guaranteed lower limit voltage to an operation-guaranteed upper limit voltage. For example, Patent Literature 1 proposes control of equalizing voltages of a plurality of power storage elements by measuring the voltage for each of the plurality of power storage elements, and selectively discharging a high-voltage power storage element.